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doc.madani
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I was wondering, when planes are flying at an altittude of 10km above sea level,, does the Earth's rotational spin affect the planes velocity? e.g. fly against rotational spin would it increase the velocity of the plane?
The unit of knots is simply a measure of speed. It has nothing to do with relative ground speed or airspeed. It is equivalent to 1 nautical mile per hour.tony873004 said:This is why the speed of planes (and boats too) are measured in knots rather than mph or km/hr. Knots tells you how fast you are moving relative to the air, (or in the case of a boat, the water), rather than ground speed.
Spaceships launched at the equator get an extra 1000 mph boost that they would not have if they were launched from the poles. Additionally, launching from the equator allows you to launch into an orbit of any inclination, from equatorial to polar. Launching from the poles only allows you to enter polar orbits (without burning a lot of fuel correcting).doc.madani said:ohh thank you i understand now :)
that's why spaceship launches are situated closer to the equator in which they can utilize the Earth's rotational spin more efficiently
Thanks for the correction.FredGarvin said:The unit of knots is simply a measure of speed. It has nothing to do with relative ground speed or airspeed. It is equivalent to 1 nautical mile per hour.
Can you please clarify this second statement? Other than the extra 1000mph, I don't see how it is any easier to go from an equatorial launch to a polar orbit than it is to go from a polar launch to an equatorial orbit. Either way, you burn the same fuel to alter your orbit.tony873004 said:Spaceships launched at the equator get an extra 1000 mph boost that they would not have if they were launched from the poles. Additionally, launching from the equator allows you to launch into an orbit of any inclination, from equatorial to polar. Launching from the poles only allows you to enter polar orbits (without burning a lot of fuel correcting).
DaveC426913 said:Can you please clarify this second statement? Other than the extra 1000mph, I don't see how it is any easier to go from an equatorial launch to a polar orbit than it is to go from a polar launch to an equatorial orbit. Either way, you burn the same fuel to alter your orbit.
I can see if you're suggesting that the 1000mph would make it easier, sure, but your second statement said "additionally", suggesting it is cumulative with the first. I think that you're double-dipping.
They only get an extra 1000 mph boost at the equator if they are launching into a prograde equatorial orbit. For any other inclination, only the projection of the velocity due to Earth rotation onto the desired orbital plane is of use. The component of that initial velocity due to Earth rotation that is normal to the desired orbital plan is worse than useless. It has to be negated by the rocket. For an inclination of 45 degrees or more, it is better to launch from somewhere other than the equator. For a polar orbit, the best place to launch is somewhere far in the north.tony873004 said:Spaceships launched at the equator get an extra 1000 mph boost that they would not have if they were launched from the poles.
Right. I shouldn't log in from work. Can't think.willem2 said:you can fly a polar orbit from the equator by starting of north or southwards. your extra 1000mph will be wasted. If you set of from the pole the only way to get into an equitorial orbit, is to fly to the equator and kill all your north/south velocity and start of accelerating east or westwards
I agree with all this. But the OP asked why we have launches situated from close to the equator. Pretty much it's because we are attempting to launch into near-equatorial, prograde orbits.D H said:They only get an extra 1000 mph boost at the equator if they are launching into a prograde equatorial orbit. For any other inclination, only the projection of the velocity due to Earth rotation onto the desired orbital plane is of use. The component of that initial velocity due to Earth rotation that is normal to the desired orbital plan is worse than useless. It has to be negated by the rocket. For an inclination of 45 degrees or more, it is better to launch from somewhere other than the equator. For a polar orbit, the best place to launch is somewhere far in the north.
Aside: Most polar orbiters are not in a true polar orbit. They are in an orbit with an inclination greater than 90 so they can be sun synchronous. Launching from the equator into a 98 degree orbit is downright silly.
Such a method would measure the speed relative to the water, rather than relative to Earth's surface. This is probably how it was once explained to me, which is why I assumed it was speed relative to the air or water mass. But as Fred pointed out, (and Wiki agrees with him :) ), it's simply a measure of speed.nucleus said:The word Knots goes back to the sailing days. They used to have a rope with knots tied in it a certain distance apart. This rope was wound on a drum and the other end contained a wooden block that would drag in the water. By counting the number of knots in a certain time they could get a measure of speed.
doc.madani said:I was wondering, when planes are flying at an altittude of 10km above sea level,, does the Earth's rotational spin affect the planes velocity? e.g. fly against rotational spin would it increase the velocity of the plane?
Sure it does, in two ways. The first is so obvious that no one has mentioned it yet: The Earth's atmosphere rotates with the planet, more-or-less. The second way in which the Earth's rotation effects the velocity of a plane relative to the Earth is that expressing velocity with respect to the surface of the Earth means that one is working in a rotating reference frame. One of the terms in the equations of motion for a rotating reference frame is the Coriolis acceleration, [itex]-2\boldsymbol{\Omega}\times\mathbf v[/itex].Cleonis said:The fact that the Earth rotates has no effect on the velocity of planes relative to the Earth.
This contradicts your initial statement. The Eötvös effect is simply the vertical component of the Coriolis acceleration.Cleonis said:In geophysics this rotation-of-Earth effect is called the Eötvös effect, after the geophysicist Eötvös.
Cleonis said:The fact that the Earth rotates has no effect on the velocity of planes relative to the Earth.
D H said:Sure it does, in two ways.
Cleonis said:In geophysics this rotation-of-Earth effect is called the Eötvös effect, after the geophysicist Eötvös. He first noticed the effect in gravimetric readings that had been taken onboard a sailing vessel. Al over the world many gravimetric readings had been taken. Readings during motion westward were consistently somewhat higher than when moving eastward.
D H said:The Eötvös effect is simply the vertical component of the Coriolis acceleration.
So what? The centrifugal and coriolis forces don't do work. That does not mean that these apparent forces do not affect the behavior of a plane. It just means that the effect does not exhibit itself in the form of a change in energy.Cleonis said:Question: the amount of work that the propulsion must do to bring the airplane up to speed, is it the same on a non-rotating and a rotating planet? Yes, it's the same: it's the change of velocity that matters. That is: changing velocity from 1600 km/h to 1700 km/h requires the same amount of work als changing velocity from 0 km/h to 100 km/h.
D H said:The centrifugal and coriolis forces don't do work. That does not mean that these apparent forces do not affect the behavior of a plane. It just means that the effect does not exhibit itself in the form of a change in energy.
The Coriolis effect is the apparent deflection of objects (including planes) from a straight path due to the rotation of the Earth. It is caused by the difference in rotational speeds of different latitudes on the Earth's surface.
The Coriolis effect affects planes by causing them to veer off course, especially on long-distance flights. This is because the Earth's rotation causes air currents to move in curved paths, which can impact the direction and speed of the plane.
No, the Coriolis effect alone cannot cause plane crashes. Pilots are trained to account for the Coriolis effect and adjust their flight paths accordingly. Other factors such as weather conditions and human error are more likely to cause plane crashes.
Yes, the Coriolis effect affects planes in both hemispheres. In the Northern Hemisphere, the deflection is to the right, while in the Southern Hemisphere, it is to the left. This is due to the direction of the Earth's rotation.
Yes, besides the Coriolis effect, the Earth's rotation can also affect planes through the centrifugal force caused by the Earth's spin. This can cause uneven distribution of weight and can impact the plane's performance, especially on long-distance flights.